[Ptb]

I have a problem with my CP5176: it only compresses in the 20:1 (SLAM) mode. In all other ratio settings (4:1, 8:1, 12:1) there is no audible compression and the gain reduction meter does not move, even with high input level.

All calibrations have been done according to the manual and the values are correct. The unit passes audio fine and sounds good in 20:1, but the other ratios seem inactive.

[JPK]

Can you do the measurements shown in 4. Check the side chain in this page?

[Ptb]

Thanks, here are the measurements

AC level on TP3:

• Ratio 2 : 0.65 VAC = 3,3
• Ratio 4 : 1.3 VAC = 6,58
• Ratio 8 : 2.1 VAC =  9,04
• Ratio 12 : 3.4 VAC = 11,02
• Ratio 20 : 5.9  VAC = 11,69
• Ratio SLAM : 6.6 VAC = 9,56

DC level on TP4:

• Ratio 2 : 0 VDC = 0
• Ratio 4 : -0.5 VDC = -0,5
• Ratio 8 : -1.3 VDC = -1,3
• Ratio 12 : -2.5 VDC = -2,5
• Ratio 20 : -5.5 VDC = -5,5
• Ratio SLAM : -0.6 VDC = -0,6

DC level on JMP1 pin 1:

• Ratio 2 : 0.6 VDC = 0,7
• Ratio 4 : 0.9 VDC = 14,42
• Ratio 8 : 1.2 VDC = 12,3
• Ratio 12 : 1.9 VDC = 11,78
• Ratio 20 : 2.3 VDC = 9,17
• Ratio SLAM : 7.9 VDC = 13,8

DC level on TP6:
      -4.5 to -1.2 VDC depending on P6 = -13,2

DC level on TP5 with jumpers JMP1 on 2-3 and 4-5 [o o-o o-o]:
      0.32 VDC =  0,32 

A 12,7
B -0,6
C 13,3
D -0,2
E 15
F -0,8
G -15,1

[JPK]

With the same conditions as in 4. Check the side chain
What AC voltage do you get on U1 pin1 (1.4VAC) and U1 pin5 (0.7VAC) ?

Check the solder joints and value of resistors R25, R27, R33, R34, R35.

[Ptb]

Measurements: U1 pin 1 = 1.10 VAC, U1 pin 5 = 0.55 VAC.

I inspected the solder joints around U1 and the checked resistors; solder joints look OK and the resistor values (R25, R27, R33, R34, R35) match the values.

[JPK]

The problem lies around U1-U2, R33, R34, R35 and maybe R28 to R32.
The signal gain between U1-pin5 and TP3 should go from 1 to 9, depending on the ratio switch.
Your gain goes from 6 to 21. The gain is based on these resistors.